Liposome having inner water phase containing sulfobutyl ether cyclodextrin salt

ABSTRACT

A liposome comprising bilayer and inner water phase is disclosed. Said inner water phase may contain sulfobutyl ether cyclodextrin and an active compound.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 13/502,776, filed on Apr. 19, 2012, theentire contents of which are incorporated herein by reference andpriority to which is hereby claimed. Application Ser. No. 13/502,776 isthe U.S. National stage of application No. PCT/CN2010/078115, filed Oct.26, 2010. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) ishereby claimed from Chinese Application No. 200910075783.9, filed Oct.26, 2009, the disclosure of which is also incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a liposome having inner water phasecontaining sulfobutyl ether cyclodextrin salt, to methods formanufacturing the liposome and to the use thereof in preparing amedicament for the treatment of tumor diseases.

BACKGROUND OF THE INVENTION

As a carrier of drugs, a liposome has the characteristics such asenhancing therapeutic efficacy, reducing adverse effects, targetdelivering, and delayed release. Especially where a liposome is used asthe carrier of anti-tumor drug, the drug can be targetedly delivered totumor area and thus has reduced toxicity and enhanced efficacy.

There are many anti-tumor drugs in clinical application which can becategorized into 5 groups: cytotoxic agents, hormones, biologicalresponse modifier, monoclonal antibodies and other anti-tumor drugs.Among them, cytotoxic agents capture the biggest market share, and theycan be categorized into 5 groups according to mechanism of action: (1)drugs acting on DNA chemical structure, such as alkylating agents andplatinum compounds; (2) drugs modifying nucleic acid synthesis, such asmethotrexate and fluorouracil; (3) drugs acting on nucleic acidtranscription, such as doxorubicin and epidoxorubicin; (4) drugs actingon tubulin synthesis, such as taxanes and vinca alkaloids; drugs actingon topoisomerase, such as camptothecin; (5) other cytotoxic drugs. Amongthem, the drugs of groups (2) and (4) are of cell cycle-specificcharacter, can only kill cells in specific period of malignant tumorcell proliferation cycle. Vinorelbine and topotecan are of the groupsand are intensively investigated in the present invention.

It is necessary to control the drug release from liposome with the aimof reducing toxicity and enhancing efficacy, where anti-tumor drug withcell cycle-specific character is prepared into liposome. In case of toofast drug releases from liposome, the following results will beincurred: (1) part of drug is released from liposome before reachingtumor area and is cleared from blood too quickly to reach tumor area;(2) in view that tumor cells are in different growth periods at the sametime, the drug reaching tumor area can not kill cells out of specificperiods, which induces greatly reduced exposure of the drug to tumorcells and has a poor therapeutic efficacy but induces toxic response ofnormal tissues. So it is important to control the drug release fromliposome especially for the drugs with cell cycle-specific character.

The release of liposomal drug is influenced by diversified factorsincluding particle size, lipid membrane composition, inner water phaseand methods of drug loading, inter alia. Methods of drug loading includeactive drug loading and passive drug loading. Passive drug loading isgenerally suitable for lipid-soluble drugs, while active drug loading isgenerally suitable for water-soluble drugs. Since vinorelbine andtopotecan are both water-soluble weak alkalescent drugs, active drugloading is chosen to prepare their liposomes. Three methods of activedrug loading are commonly used in the art: pH gradient method, ammoniumsulfate gradient method and complexation gradient method.

(1) pH Gradient Method:

This method is invented by Canadian investigators in the 1980's. Theydiscovered that pharmaceutical alkaloids such as doxorubicin could beactively transported and specifically aggregated into liposomes in thepresence of pH gradient. The first thing in the process of preparationis to choose inner water phase buffer and outer phase buffer, which iscritical since the buffers directly determines the stability of drug instorage and the release of drug in vivo. A blank liposome is formed byhydration with inner water phase buffer. The thus-obtained blankliposome is further processed to reduce the particle size within adesired range. Next, outer phase of the liposome may be replaced byusing the technical means such as cross flow dialysis, columnchromatography and pH modulation, so as to form pH gradient betweenouter and inner transmembrane phases. The drug loading may beaccomplished at an appropriate temperature after the transmembranegradient is formed.

Also the transmembrane pH gradient can be formed using an ionophore.During the preparation of the blank liposome, divalent ion salt, such asmanganese sulfate, is encapsulated into the liposome, and then the outerphase of liposome is replaced by a buffer containing an ionophore, suchas A23187 and EDTA. The ionophore can specifically transport divalention to outside of membrane and transport H⁺ to inside of liposome. Useof the above method can also form pH gradient between inside and outsideof the membrane.

The mechanism of drug loading by pH gradient has been intensivelyinvestigated. Among 3 anthracycline liposome preparations available inthe market, 2 preparations are prepared by active drug loading using pHgradient.

(2) Ammonium Sulfate Gradient Method

Ammonium sulfate gradient method is invented by Israeli investigators inearly 1990's. The preparation process in this method is similar to thatin traditional pH gradient method. First, blank liposome is prepared byusing ammonium sulfate buffer. Then, ammonium sulfate in outer phase ofthe liposome is removed by cross flow dialysis inter alia to formammonium sulfate gradient between the inside and the outside of lipidmembrane. Then drug loading is accomplished under the condition ofheating. It is confirmed in initial research that the drug loading byammonium sulfate gradient may be related to pH difference between theinside and the outside of the phospholipid membrane caused bytransmembrane diffusion of free ammonia. However, it is shown by stricttheoretical deduction that the drug loading using ammonium sulfategradient method may be a complicated process of double-directionaldiffusion, and the formation of pH gradient may be merely one of thefactors.

The advantage of ammonium sulfate gradient method lies in thatapproximately neutral pH of the ammonium sulfate aqueous solution couldnot induce hydrolyzation of excess phospholipid molecules, because arelatively high temperature is required if saturated phospholipid isused to prepare the liposome. The lipid is apt to hydrolyze whentraditional pH gradient method is used. Moreover, the in vivo drugrelease of the liposome prepared using ammonium gradient method may bedifferent.

(3) Complexation Gradient Method

In this method, transition metal ion salt, such as copper sulfate ornickel sulfate is used in inner water phase buffer to prepare blankliposome. Next, metal ion outside the liposome is removed by cross flowdialysis among others to form the metal ion gradient between the insideand the outside of lipid membrane. Then drug loading is accomplishedunder the condition of heating. The mechanism of drug loading is thatthe drug forms a stable complex with transition metal ion in the innerwater phase of liposome and is thus restrained within liposome.

As the first-line drugs in anti-tumor therapy, liposomal preparations ofvinorelbine and topotecan have been intensively investigated. Now thedrug loading of liposomal vinorelbine and topotecan have beeninvestigated by many research groups. However, some problems rise suchas the following:

Inex company of Canada achieves the drug loading by using sphingomyelinand cholesterol at a molar ratio of 55:45 as lipid membrane, using asolution of magnesium sulfate (450 mM) as inner water phase to prepareblank liposome, then transporting magnesium ion out of the liposomalmembrane via the ionophore A23187 (the amount of added ionophore is 1μg/mg lipid), and transporting H⁺ to inside of liposome, and thusgenerating pH gradient. The thus-obtained liposomal vinorelbine has anencapsulation rate of more than 90%, and is stable when stored at 2-8°C. for one year. Because the ionophore can be toxic to cells andanimals, it is necessary to strictly control the residue of ionophore inthe formulation. The researchers need to perform a further dialysis onthe liquid after the drug loading is completed, so that the finalresidue of ionophore in the final liquid is less than the usuallyaccepted safety standard, 50 ng/mg phospholipid. (Optimization andcharacterization of a sphingomyelin/cholesterol liposome formulation ofvinorelbine with promising antitumor activity. Journal of PharmaceuticalSciences, 2005 Vol. 94 No. 5.)

A Canadian research group leaded by Bally used two methods and obtainedtopotecan liposomes having high encapsulation rate. In the first method,DSPC and cholesterol are used as lipid membrane, a 300 mM solution ofmanganese sulfate or manganese chloride as inner water phase to preparea blank liposome. Then pH gradient is formed using the ionophore A23187and the drug loading is achieved.

The amount of added ionophores was 250 ng/mg lipid. The mechanism ofthis method is similar to that used by Inex company. But this method didnot perform the step of removing ionophores after drug was loaded, sothe residual metal ions in the preparation may produce toxicity in theblood. The second method uses DSPC and cholesterol as lipid membrane,copper sulfate solution as inner water phase to prepare blank liposome.However, the loading of topotecan is accomplished without adding A23187,because a stable complex is formed between copper ion and topotecan. Theprinciple used herein is just the complexation gradient method asdescribed above. (An evaluation of transmembrane ion gradient-mediatedencapsulation of topotecan within liposomes. Journal of ControlledRelease. 96 (2004); Copper-topotecan complexation mediates drugaccumulation into liposomes. Journal of Controlled Release. 114 (2006)).

US investigators use distearoyl phosphatidyl choline (DSPC), cholesteroland distearoyl phosphatidyl ethanolamine-methoxyl-polyethylene glycolconjugate (DSPE-mPEG) as lipid membrane, use triethylamine (TA) salt ofsucrose octasulfate as inner water phase to prepare blank liposome. ThenTA sucrose octasulfate is removed using cross flow dialysis inter aliato form TA sucrose octasulfate gradient, and the loading of drug isaccomplished. The principle is substantively identical to that used inammonium sulfate gradient method. However, each sucrose octasulfatemolecular has 8 acid groups and can form a tight complex withvinorelbine, and thus vinorelbine is well restrained. The plasmahalf-life of the thus-obtained vinorelbine liposome is up to 9.2 hours(Improved pharmacokinetics and efficacy of a highly stable nanoliposomalvinorelbine. The journal of Pharmacology and Experimental Therapeutics.2009 Vol. 328 No. 1.). The serious concern in this method is thatsucrose octasulfate is physiologically active and activates fibroblastgrowth factor in vivo (Structural basis for activation of fibroblastgrowth factor signaling by sucrose octasulfate. MOLECULAR AND CELLULARBIOLOGY, Oct. 2002, Vol. 22, No. 20), and induce a series ofphysiological effects. Therefore, the use of sucrose octasulfate as anexcipient for injection may have a great risk.

Alza company of US uses hydrogenated soybean phosphatidyl choline(HSPC), cholesterol and DSPE-mPEG as lipid membrane, uses polyanionpolymer, such as dextran sulphate, proteoglycan sulphate and cellulosesulphate, in inner water phase. Then cross flow dialysis is used toreplace outer phase and form a polymer gradient, and the drug loading isaccomplished. The principle is similar to that used in ammonium sulfategradient method. This method has the aim of forming a tight complex ofpolyanion polymer with topotecan, and thus the drug is well restrained.The disadvantage of this method is also that the polyanion polymers arephysiologically active and difficult to be metabolized in vivo, so thesafety thereof shall be further investigated (Liposome-entrappedtopoisomerase inhibitors. US6465008B1).

It is known from the above that the investigations of liposomes of weakalkalescent drugs, such as vinorelbine and topotecan focus on pHgradient method, general ammonium sulfate gradient method andcomplexation gradient method. However, they are only tested inlaboratory and the materials used have safety risk: (1) the polyanionicsalt, such as triethylamine salt of sucrose octasulfate and sulfatepolymer, used in the above investigations are all physiologicallyactive, and do not meet the requirement that an excipient should beinactive of physiology and of pharmacology; (2) copper ion, nickel ion,manganese ion used in the above complexation gradient method are allheavy metal ion, and their remainder in the formulation are harmful tohuman. Moreover, because tumor is difficult to be cured and medicationis generally a long time, the in vivo accumulation of heavy metal ionwill go beyond the patient tolerance.

So it is still required to develop a novel liposome and correspondingmethod of drug loading.

SUMMARY OF THE INVENTION

The inventors have surprisingly found in the study that liposomes can beprepared by SBE-β3-CD, in order to achieve the effective seal andloading of active ingredient. In the invention, the SBE-β3-CD functionscompletely different from the cyclodextrin in the liposome inclusion inthe prior art. In the present invention, the inventors break through thetraditional thinking way, and use the polyanionic property of SBE-β3-CD,instead of using its cage-shape characteristic and forming an inclusionand then passive loading of drug. Specifically, a blank liposomecomprising sulfobutyl ether cyclodextrin ammonium salt or metal saltsthereof in the inner phase is firstly prepared, then the salt ofsulfobutyl ether cyclodextrin in the outer phase of the blank liposomeis removed, to form an anion gradient, and a metal cation ionophore isadded to the outer phase of the blank liposome, to form a pH gradient,so as to load active ingredient actively. The present invention isparticularly suitable for water soluble drugs, such as doxorubicinhydrochloride, topotecan hydrochloride, vincristine sulfate and thelike, since they can enter into the inner water phase of the liposomewithout need to be prepared into a cyclodextrin inclusion, thus a goodencapsulation can be achieved. If the water soluble drugs if only relyon the inclusion effect of the SBE-β3-CD, the liposome entrapmentefficiency will be very low, which has been demonstrated in the workingexamples of the present invention. In fact, the purpose of the inventionis not to solve the problem of entrapment of insoluble drugs, but toextend the residence time of water soluble alkalescence drugs in aliposome, so as to meet the clinical requirements.

The use of sulfobutyl ether cyclodextrin salt as inner water phase toload drug has a similar principle as that in the use of ammonium sulfateas inner water phase, by which the anion in inner water phase formsprecipitate with the drug molecule and thus extend drug release.However, each sulfobutyl ether molecule has 6.5 SO₃ ²⁻ at average, andcan bind to multiple drug molecules simultaneously and form more complexprecipitate structure. So high encapsulation rate is achieved, and thedrug retention time is significantly extended in comparison to theliposome with ammonium sulfate as inner water phase.

On the other hand, compared with the pH value gradient method and thecomplex gradient method used in the prior art, the method of the presentinvention adopts the combination of the salt of SBE-CD and metal cationionophores, allowing a lower addition amount (as low as 20 ng/mg lipid)of the ionophores, while achieving the same or better encapsulationeffect, which is of great significance for the safety applicationespecially for long-term application of a drug. Furthermore, the methodof the present invention can save the further dialysis step, thus savethe production time and cost, but also reduce the risk of penetration ofdrug during the dialysis process.

Specifically, in the present invention, a metal ion salt of SBE-CD, suchas a sodium salt, a calcium salt, a magnesium salt, is used as inneraqueous phase of the liposome, and then ionophores that can transfer thecorresponding ions are added to form a pH gradient, thus drug loading isachieved. The concentration of liposome inner aqueous phase SBE-CD inthe present invention is comparable to that of sulfate and chloride ofthe prior art, but addition amount of metal cation ionophore is only 20ng/mg lipid, which is far less than the amount 250 ng/mg lipid or 1ug/mg lipid in the background technology, however, it can achieve anentrapment rate greater than 90%, which shows that the present inventioncan achieve an unexpected effect by using SBE-CD, which causes acomplexation of the drug much stronger than the sulfate and chloride. Inthe prior art, due to a relatively high amount of ionophores, it may betoxic to cells and animals. The initial addition amount of the metalcation ionophore in the present invention is far less than the criticalvalue of 50 ng/mg phospholipid generally accepted, so the presentinvention can save the further dialysis step.

Without limited by the theory, the following contents will attempt toexplore the mechanisms related to drug loading methods in the priorarts. Firstly, the ammonium sulfate gradient method is analyzed, whichcomprises the following process: driven by concentration and pHdifference, high-concentration drug in outer phase of the liposomeovercomes resistance of lipid membrane (phospholipid bilayer) and comesinto the inner water phase of the liposome. The drug which comes intothe inner water phase is protonated and precipitates with SO₄ ²⁻, and isrestrained stably in the liposome. It is needed to dissociate from theprecipitate and diffuse out from the liposome for drug release.Therefore, the microscopic structure and solubility of the precipitatedetermine the release rate of drug from the liposome and furtherdetermine the safety and effectiveness of the formulation.

The microscopic structure and complexity of the precipitate formed bythe drug and SO₄ ²⁻ are related to the spatial structure and weakalkalescence of the drug. Some drug, such as doxorubicin hydrochloride,is apt to form precipitate with SO₄ ²⁻ due to its strong alkalescence.Moreover, the drug molecules can pile up on each other due toquasi-planar structure of the molecule. and a compact elongatedprecipitate is formed within the liposome as microscopically shown.Therefore, doxorubicin hydrochloride can be well restrained in theliposome and the half-life t_(1/2) of its liposomal formulation in KMmice is more than 15 hours. To the contrary, other drugs, such asvinorelbine and topotecan, are weak alkalescent and thus have a poorability to precipitate with SO₄ ²⁻, and the drug molecules can not pileup on each other due to non-planar structure of the molecule. Therefore,the t_(1/2) in KM mice is less than 5 hours even if the liposome isprepared by using the same lipid composition and method as those of theabove doxorubicin hydrochloride liposome. The half-life is so short thatmost of the drug leaked out from the liposome in blood circulation andcan not reach tumor area. Even a small ratio of the liposomal drug whichreached tumor area will be released out quickly. It is undesired foranti-tumor drug with cell cycle-specific character to exert its effect.It is concluded that one of the critical factors for drug release is thecomplexity of the precipitate formed between drug and anion.

The ammonium sulfate gradient method is relatively suitable foranthracycline anticancer drugs having a planar structure (such asdoxorubicin (adriamycin), epirubicin, pirarubicin, idarubicin,mitoxantrone), because they can achieve the intermolecular piling, andthen form a strip dense precipitation with the salt in the inner phase,which facilitates the drug entrapment and retention.

As for the weakly alkalescent drugs vinorelbine, topotecan etc, becauseof their inherent weak alkalinity, they are not suitable for theammonium sulfate gradient method, so an anion that can combine withthese drugs and form dense precipitation becomes the key to solve theproblem, and the multi anionic compounds with complex structure may beused to produce more stable complex.

It is experimentally demonstrated that efficient encapsulation of weakalkalescent drug, such as vinorelbine or topotecan, can be achieved inthe present invention. In vitro release test and pharmacokinetic testconfirm that, in comparison to the conventional ammonium sulfate innerwater phase formulation, the release rate of the liposomal drug of thepresent invention is markedly extended. The present invention is alsosuitable for other anti-tumor drugs, such as vincristine and irinotecan,with similar weak alkalescence of vinorelbine and topotecan.

Sulfobutyl ether-β-cyclodextrin (SBE-β-CD) is an ionized derivative ofβ-cyclodextrin (β-CD) developed by Cydex of US in 1990's, which is theproduct of substitution reaction of β-CD with 1,4-butane sultone. Thesubstitution may occur at hydroxyl group of position 2, 3, 6 in glucoseunit of SBE-β-CD. SBE-β-CD is an excellent pharmaceutical excipienthaving the advantages such as good water-solubility, low nephrotoxicityand low haemolysis, and is licensed by FDA as an excipient forinjection.

SBE-β-CD has a spacial steric configuration of cyclic cage structure,with hydrophilic shell and hydrophoric inner room, and has been so farused for solubilization by inclusion of many insoluble drugs, thusachieve solubilization of insoluble drugs in hydrophilic solvents, andhas been used widely in various dosage forms such as injection, oralformulation, topical formulation inter alia. Wang Zhixuan & DengYingjie, et al. (Advances in liposome entrapped drug cyclodextrincomplex delivery systems, Journal of Shenyang Pharmaceutical University,2006 Vol. 23) review world-wide researches of liposome entrapped drugcyclodextrin complex. Fat soluble or water insoluble drug can not enterthe inner water phase of liposome, thus it is usually present in thelipid bilayer membrane. Such an existing way has the followingshortcomings, first it will affect the stability of membrane structure,then it limits loading amount of drug. If the insoluble drug is firstprepared into a cyclodextrin inclusion which is water-soluble, and thenthe inclusion is entrapped in the inner aqueous phase of liposomes, theabove problem can be solved. The liposome of this structure is called ascyclodextrin inclusion liposome.

Chakraborty used SBE-β-CD to investigate liposomal preparation ofamphotericin B, with the aim of using solubilization by inclusion ofinsoluble drug by SBE-β-CD, and obtained a amphotericin B liposome withhigh inclusion rate and high drug loading (Therapeutic and hemolyticevaluation of in-situ liposomal preparation containing amphotericin-Bcomplexed with different chemically modified β-cyclodextrins. J PharmPharmaceut Sci. 2003 Vol. 6, No. 2).

US patent application 2007/0014845 recites a method for preparingliposome, comprising first preparing a cyclodextrin inclusion of acompound, and then loading the inclusion into liposomes, wherein thecompound is a hydrophobic compound, including proteins, peptides,nucleic acids, diagnostic reagents, cardiovascular drugs, antibiotics,cytotoxic drugs and the like. It is indicated in paragraph 0005 that theconcentration of cyclodextrin in the cyclodexrin inclusion liposomeshould be greater than 100 mg/ml, and most preferably 400 mg/ml. In thepresent invention, the concentration of SBE-β-CD in the inner phase ofthe sulfobutyl ether cyclodextrin prepared is 80-200 mg/ml,significantly less than the concentration used in the US patentapplication, but can get better encapsulation efficiency. The USapplication recites in the paragraph 0022-0023 of the descriptionrecords that the cyclodextrin in the cyclodextrin inclusion liposome isselected from a variety of cyclodextrin derivatives, including theSBE-β-CD sodium salt; and the drug is entrapped in the aqueous phaseafter formation of a inclusion with cyclodextrin. In the method of thepresent invention, the liposomes comprising sulfobutyl ethercyclodextrin in the inner phase can also adopt the SBE-β-CD sodium saltas the inner aqueous phase, however, for the method of the presentinvention, after the formation of blank liposomes comprising SBE-β-CDsodium salt in the water phase, metal cation ionophores are added, andsodium ions in the lipid membrane are pumped out, and hydrogen ionsouter of the lipid membrane are pumped in, thus forming transmembrane pHgradient, so as to achieve the drug loading. The US applicationexplicitly teaches that suitable drugs are the fat soluble drugs,including topoisomerase I inhibitors, such as camptothecin,hydroxycamptothecin, sn38 etc. In addition, the US patent applicationmethod has a very high loss rate of drug, for example, as recited inexample 2 thereof, in the preparation process of liposomes, the lossrate of drug is as high as 81.5%, the reason might be the following: theinner phase of the liposome obtained by hydration only accounts for avery small part of the total volume, due to the inclusion of the drugand cyclodextrin as phospholipid hydration solution, while most of thedrug inclusion in the outer aqueous phase of the liposome are removed inthe following dialysis steps, so this method of passive loading isdifficult to achieve good encapsulation of hydrophobic drugs.

To obtain liposomal preparations with good properties, a salt ofsulfobutyl ether cyclodextrin should be prepared first, and then theliposome should be prepared using a proper method. The method used inthe present invention comprises:

(A) Preparation of salts of sulfobutyl ether cyclodextrin: preparingaqueous solution of sulfobutyl ether cyclodextrin, and salifying withtriethylamine, triethanolamine, ammonia, sodium hydroxide, potassiumhydroxide or calcium hydroxide.

(B) Preparation of liposomes: dissolving lipid excipients in an organicsolvent, removing the organic solvent by lyophilization and thenobtaining a loose lipid powder, hydrating the lipid phase powder withaqueous solution of sulfobutyl ether cyclodextrin salt to form a blankliposome. Then reducing the particle size of the blank liposome by amicro-jet apparatus or a high pressure extrusion apparatus, removing thesalt of sulfobutyl ether cyclodextrin in outer phase of the liposome bydialysis or column chromatography inter alia to form an aniontransmembrane gradient. If the salt of sulfobutyl ether cyclodextrinused is a metal ion salt, the addition of metal ionophore is required.The metal ionophore can be inserted into phospholipid membrane toexchange internal metal ion and external hydrogen ion, and thus a pHgradient is formed. Then the liposomal preparation is obtained byincubation the drug solution and the liposome suspension.

Sulfobutyl ether cyclodextrin used in the present invention shall beimported currently. However, it can be produced in bulk with goodquality and meet the need of large scale production.

In summary, in the present invention, use of salts of sulfobutyl ethercyclodextrin as liposome inner water phase is completely feasible inconsideration of drug encapsulation, retention effect and economic cost.

According to some embodiments of the liposome in the present invention,wherein the sulfobutyl ether cyclodextrin is sulfobutylether-α-cyclodextrin, sulfobutyl ether-β-cyclodextrin or sulfobutylether-γ-cyclodextrin.

According to some embodiments of the liposome in the present invention,wherein each sulfobutyl ether cyclodextrin molecule has about 6.5 sulfogroups at average.

According to some embodiments of the liposome in the present invention,wherein the salt of sulfobutyl ether cyclodextrin is formed bysulfobutyl ether cyclodextrin with one or more of amine, metal ion andammonium ion.

According to some embodiments of the liposome in the present invention,wherein the salt of sulfobutyl ether cyclodextrin is formed bysulfobutyl ether cyclodextrin with one or more of ammonia (NH₃),triethylamine (TA), triethanolamine (TEA), sodium ion, potassium ion andcalcium ion.

According to some embodiments of the liposome in the present invention,wherein the active compound is an weak alkalescent compound, preferablyone or more selected from vinorelbine, vincristine, topotecan andirinotecan.

According to some embodiments of the liposome in the present invention,wherein the bilayer comprises phospholipid, cholesterol and hydrophilicpolymer-modified lipid.

In the present invention, any suitable metal cation ionophores known inthe field can be used, such as nikkomycin, A23187 and ionomycin.

In another aspect, the present invention provides a process forpreparing the liposome of the present invention described above,comprising:

(1) hydrating lipid phase powders with aqueous solution of sulfobutylether cyclodextrin or its salt, to form a blank liposome comprising theaqueous solution of sulfobutyl ether cyclodextrin or its salt as innerwater phase,

(2) removing the salt of sulfobutyl ether cyclodextrin in the outerphase of the blank liposome obtained in step (1), to form an aniongradient,

(3) adding a metal cation ionophore to the outer phase of the blankliposome, to form a pH gradient, and

(4) incubating the blank liposome obtained in step (3) with the activecompound in aqueous solution, to encapsulate the active compound intothe liposome.

According to a preferred aspect of the preparation method of the presentinvention, the metal casion ionophore is ionophore A23187.

In a further aspect, the present invention provides a liposomalpharmaceutical preparation, comprising the liposome according to any ofthe present invention described above and a pharmaceutically acceptablecarrier and/or excipient.

According to some embodiments of the liposomal pharmaceuticalpreparation in the present invention, wherein the carrier and/orexcipient comprises osmotic regulator and/or antioxidant.

In another further aspect, the present invention provides use of theliposome according to any of the present invention described above inmanufacture of a medicament for treatment of a tumor in a patient,wherein the active compound in the liposome is one or more ofvinorelbine, vincristine, topotecan and irinotecan.

DESCRIPTION OF THE DRAWINGS

FIG. 1 indicates the in vitro release results of doxorubicin liposomescomparing different inner phases;

FIG. 2 indicates the in vitro release results of mitoxantrone liposomescomparing different inner phases;

FIG. 3 indicates the in vitro release results of topotecan liposomescomparing different inner phases;

FIG. 4 indicates the in vitro release results of irinotecan liposomescomparing different inner phases.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is illustrated by the following examples, which isonly exemplary and should not be construed as a limitation to the scopeof the present invention.

As used herein, the drug/lipid ratio refers to weight ratio of drug tophospholipid, and “the content of DSPE-mPEG” Refers to its molarpercentage in the total phospholipid components in liposomal bilayer.

Example 1 General Process of Preparation of Liposomes with SulfobutylEther Cyclodextrin (SBE-CD) as Inner Water Phase (with the Formulationof SBE-CD)

HSPC, cholesterol and DSPE-mPEG2000 at a mass ratio of 3:1:1 were mixedand dissolved in 95% t-butyl alcohol. The organic solvent was removed bylyophilization to obtain a loose lipid powder. The powder was hydratedwith aqueous solution of sulfobutyl ether β-cyclodextrin at 50-60° C.and incubated for 1 hour to obtain a heterogenous multivesicularliposome. The particle size of the liposome was reduced by a micro-jetapparatus. Anion in outer phase of the blank liposome was removed by anultrafiltration apparatus to form a dynamic transmembrane gradient. Anaqueous drug solution was added to the blank liposome at an appropriatedrug/lipid ratio, and the drug loading was achieved by incubation at 60°C. for 1 hour.

Example 2 General Process of Preparation of Liposomes with TriethylamineSalt of Sulfobutyl Ether Cyclodextrin as Inner Water Phase (with theFormulation of SBE-CD/TA)

HSPC, cholesterol and DSPE-mPEG2000 at a mass ratio of 3:1:1 were mixedand dissolved in 95% t-butyl alcohol. The organic solvent was removed bylyophilization to obtain a loose lipid powder. The powder was hydratedwith aqueous solution of triethylamine salt of sulfobutyl ethercyclodextrin at 50-60° C. and incubated for 1 hour to obtain aheterogenous multivesicular liposome. The particle size of the liposomewas reduced by a high pressure extrusion apparatus. Anion in outer phaseof the blank liposome was removed by an ultrafiltration apparatus toform a dynamic transmembrane gradient. An aqueous drug solution wasadded to the blank liposome at an appropriate drug/lipid ratio, and thedrug loading was achieved by incubation at 60° C. for 1 hour.

Example 3 General Process of Preparation of Liposomes with Sodium Saltof Sulfobutyl Ether Cyclodextrin as Inner Water Phase (with theFormulation of SBE-CD/Na)

HSPC, cholesterol and DSPE-mPEG2000 at a mass ratio of 3:1:1 were mixedand dissolved in 95% t-butyl alcohol. The organic solvent was removed bylyophilization to obtain a loose lipid powder. The powder was hydratedwith aqueous solution of sodium salt of sulfobutyl ether cyclodextrin at50-60° C. and incubated for 1 hour to obtain a heterogenousmultivesicular liposome. The particle size of the liposome was reducedby a high pressure extrusion apparatus. Anion in outer phase of theblank liposome was removed by column chromatography, and then ethanolsolution of nikkomycin in an appropriate amount was added (20 ngnikkomycin/1 mg HSPC). The resulting mixture was incubated at 60° C. forten minutes, so as to exchange hydrogen ion and sodium ion across theliposomal membrane, so as to form a pH gradient. An aqueous drugsolution was added to the blank liposome at an appropriate drug/lipidratio, and the drug loading was achieved by incubation at 60° C. for 1hour.

Example 4 Comparison of Encapsulation Rate of Liposomes ContainingVarious Internal Water Phase

The liposomes of various drugs with 3 respective inner water phases wereprepared as described in Example 1, 2 and 3, at a drug/lipid ratio of2:9.58 (see table 1).

TABLE 1 Effect of intraliposomal trapping agent on drug loadingEncapsulation rate of liposomes having different inner water phases (%)Drug SBE-CD SBE-CD/TA SBE-CD/Na Mitoxatrone hydrochloride 7.6 48.5 77.6Topotecan hydrochloride 4.8 63.6 74.6 Irinotecan hydrochloride 5.3 64.196.1 Doxorubicin hydrochloride 11.3 63.5 91.8 Vinorelbine bitartrate 4.738.2 75.9 Vincristine sulfate 3.8 47.8 79.7

Conclusion: as can be seen from encapsulation rate as disclosed, theliposome having SBE-CD as inner water phase has a poor encapsulationrate, while high encapsulation rates were achieved with SBE-CD/TA andSBE-CD/Na, which illustrates that a good encapsulation cannot beachieved unless a pH gradient is formed by ion transporting. The drug isfirstly protonated after entering inner water phase of the liposome, andthen associates with SBE-CD, while drug loading is hardly achieveddepending exclusively on inclusion effect of SBE-CD.

Example 5 In Vitro Release of Liposomal Vincristine FormulationsContaining Different Inner Water Phase (SBE-CD/TA Vs Ammonium Sulfate)

1, Samples

The vincristine liposomes were prepared at a drug/lipid ratio of 3:9.58,respectively as described in Example 2 for the liposome having SBE-CD/TAas inner water phase, as described in Example 3 for the liposome havingSBE-CD/Na as inner water phase, and as described in Example 2, with theexception of the replacement of sulfobutyl ether-β-cyclodextrintriethylamine salt with ammonium sulfate, for the liposome havingammonium sulfate as inner water phase.

2, Release Condition

Samples of liposomal vincristine formulations were diluted by 10 timesin release buffer (5 mM NH₄Cl/10 mM histidine/260 mM glucose, pH 7.0)and transferred into the dialysis bags. The dialysis was performedagainst a 200-fold volume of dialysis buffer in dissolution flask.Release test was performed at 37° C., 75 rpm. At various time points (1h, 2 h, 4 h, 6 h, 8 h, 24 h), aliquots were withdrawn for analysis.

3, Results

TABLE 2 Release of vincristine liposomes with different inner waterphases Drug release rate at different time (%) Inner water phase 1 h 2 h4 h 6 h 8 h 24 h t_(1/2)(h) SBE-CD/TA 22 31 44 52 61 94 7.2 SBE-CD/Na 2331 47 58 68 96 6.8 ammonium sulfate 26 62 91 97 98 99 1.1

Conclusion: In comparison to the liposome having ammonium sulfate asinner water phase, the liposome having SBE-CD/TA as inner water phaseand the liposome having SBE-CD/Na as inner water phase bothsignificantly extended the retention of drug in inner water phase.

Example 6 In Vitro Release of Liposomal Vinorelbine FormulationsContaining SBE-CD/NH₃ and Ammonium Sulfate as a Mixed Inner Water Phase

1, Samples

The vinorelbine liposomes were prepared at a drug/lipid ratio of 3:9.58,as described in Example 2 with the exception of the replacement ofsulfobutyl ether-β-cyclodextrin triethylamine salt with the mixedsolution of SBE-CD/NH₃ and ammonium sulfate as described in A-F of table3.

TABLE 3 Formulations for Liposomal Vinorelbine having SBE-CD/NH₃ andammonium sulfate as a mixed inner water phase Concentration (mM) Number[H⁺] of SBE-CD Ammonium sulfate A 280.8 86.4 B 236.7 108.9 C 204.3 126.0D 180.0 138.6 E 160.2 148.5 F 0 225.02, Release Condition

Samples of liposomal formulations were diluted by 10 times in releasebuffer (2 mM NH₄Cl/10 mM histidine/250 mM glucose, pH 7.5) andtransferred into the dialysis bags. The dialysis was performed against a200-fold volume of dialysis buffer in dissolution flask. Release testwas performed at 37° C., 75 rpm. At various time points (1 h, 2 h, 4 h,8 h), aliquots were withdrawn for analysis.

3, Results

TABLE 4 In vitro release of liposomal vinorelbine formulations havingdifferent internal water phase Sampling Release rate for different innerwater phase (%) time (h) A B C D E F 1 34.9 25.1 33.2 36.0 39.1 68.3 256.6 51.8 59.0 63.1 67.7 91.5 4 83.6 83.5 89.3 90.2 93.4 98.6 8 97.497.2 98.0 98.5 98.6 99.3

Conclusion: The liposomes having high SBE-CD/NH₃ proportion in the mixedinner water phase displayed relatively slow drug release, indicatingthat ammonium salt of SBE-CD could extend drug release.

Example 7 In Vitro Release of Liposomal Doxorubicin FormulationsContaining SBE-CD/TA, SBE-CD/Mg and Ammonium Sulfate Respectively asInner Water Phase

1, Samples

The doxorubicin liposomes were prepared at a drug/lipid ratio of 2:9.58,respectively as described in Example 2 for the liposome having SBE-CD/TAas inner water phase, as described in Example 3 (with the exception ofreplacing SBE-CD/Na with SBE-CD/Mg and replacing nikkomycin withionomycin) for the liposome having having SBE-CD/Mg as inner waterphase, and as described in Example 2 (with the exception of thereplacement of sulfobutyl ether-β-cyclodextrin triethylamine salt withammonium sulfate) for the liposome having (NH₄)₂SO₄ as inner waterphase.

2, Release Condition

Samples were diluted by 200 times in release buffer (50 mM NH₄Cl/20 mMhistidine/200 mM glucose, pH 6.5) and placed in a water bath of 52°C.±1° C. for incubation. The excitation wavelength for fluorescencespectrophotometer was set at 480 nm, and the emission wavelength at 560nm. The change of fluorescence was scanned, and the release rate wascalculated.

3, Results

TABLE 5 Result of encapsulation rate and particle size of doxorubicinliposomal comprising different inner phases Inner water phaseencapsulation rate (%) particle size (nm) (NH₄)₂SO₄ 100 94 SBE-CD/TA99.5 91 SBE-CD/Mg 99.8 93

Note: in this table, the concentration of ammonium ion in the innerwater phase of SBE-CD/TA and the concentration of Mg ion in the innerwater phase of SBE-CD/Mg were both 500 mM; the concentration of ammoniumion in the inner water phase of SBE-CD/TA in Example 4 is 300 mM; andthe concentration of sodium ion in the inner water phase of SBE-CD/Na inExample 4 is 300 mM, so the entrapment rates are different. The sameconcentration in internal water phase in the formula, similar particlesize, and entrapment rate can ensure the in vitro release data morecomparable.

Conclusion: In comparison to the liposome having ammonium sulfate asinner water phase, the liposome having SBE-CD/TA as inner water phaseand the liposome having SBE-CD/Mg as inner water phase bothsignificantly extended the retention of drug in inner water phase.

Example 8 In Vitro Release of Liposomal Mitoxantrone FormulationsContaining SBE-CD/NH₃, SBE-CD/Ca and Ammonium Sulfate Respectively asInner Water Phase

1, Samples

The mitoxantrone liposomes were prepared at a drug/lipid ratio of1:9.58, respectively as described in Example 2 (with the exception ofthe replacement of sulfobutyl ether-β-cyclodextrin triethylamine saltwith ether-β-cyclodextrin arginine salt) for the liposome havingSBE-CD/NH₃ as inner water phase, as described in Example 3 (with theexception of replacing SBE-CD/Na with SBE-CD/Ca and replacing nikkomycinwith calcimycin) for the liposome having having SBE-CD/Ca as inner waterphase, and as described in Example 2 (with the exception of thereplacement of sulfobutyl ether-β-cyclodextrin triethylamine salt withammonium sulfate) for the liposome having (NH₄)₂SO₄ as inner waterphase.

2, Release Condition

Samples were diluted by 2 times in release buffer (2 M NH₄Cl/200 mMhistidine, pH 6.5) and placed in a water bath of 52° C.±1° C. forincubation. The samples were taken respectively at time of 0, 5, 15, 30,60, 120 and 180 min, the encapsulation rates were determined, therebythe release rates can be calculated.

3, Results

TABLE 6 Result of encapsulation rate and particle size of mitoxantroneliposomal comprising different inner phases Inner water phaseencapsulation rate (%) particle size (nm) (NH₄)₂SO₄ 99.0 72 SBE-CD/NH₃99.2 73 SBE-CD/Ca 99.4 72

The results of FIG. 2 showed that compared with the liposome containingammonium sulfate as inner water phase, the liposomes containingSBE-CD/NH₃ or SBE-CD/Ca as inner water phase can significantly prolongthe retention of the drug in the inner water phase of the liposome.

Example 9 In Vitro Release of Liposomal Topotecan Formulations andLiposomal Irinotecan Formulations Containing SBE-CD/Na, SBE-CD/Ca andAmmonium Sulfate Respectively as Inner Water Phase

1, Samples

The topotecan liposomes and irinotecan liposomes were prepared at adrug/lipid ratio of 2:9.58, respectively as described in Example 3 forthe liposome having SBE-CD/Na as inner water phase, as described inExample 3 (with the exception of replacing SBE-CD/Na with SBE-CD/Ca andreplacing nikkomycin with calcimycin) for the liposome having SBE-CD/Caas inner water phase, and as described in Example 2 (with the exceptionof the replacement of sulfobutyl ether-β-cyclodextrin triethylamine saltwith ammonium sulfate) for the liposome having (NH₄)₂SO₄ as inner waterphase.

2, Release Condition

Samples were diluted by 100 times in release buffer (20 mM NH₄Cl/10 mMhistidine/250 mM glucose, pH 6.5) and placed in a water bath of 52°C.±1° C. for incubation. For topotecan, the excitation wavelength forfluorescence spectrophotometer was set at 380 nm, and the emissionwavelength at 520 nm; for irinotecan, the excitation wavelength forfluorescence spectrophotometer was set at 370 nm, and the emissionwavelength at 420 nm. The change of fluorescence was scanned, and therelease rate was calculated.

3, Results

TABLE 7 Results of encapsulation rate of topotecan liposome andirinotecan liposome comprising different inner phases encapsulation rate(%) Inner water phase topotecan irinotecan (NH₄)₂SO₄ 97.8 98.5 SBE-CD/Na98.2 98.7 SBE-CD/Ca 98.3 99.1

The results of FIG. 3 and FIG. 4 showed that compared with the liposomecontaining ammonium sulfate as inner water phase, the SBE-CD/Na andSBE-CD/Ca inner water phases can both significantly prolong theretention of the drugs in the inner water phase of the liposomes.

Example 10 Pharmacokinetics for the Liposomes Having Ammonium Sulfate,Different Ammonium Salts of SBE-CD as Inner Water Phase

1, Samples

Vinorelbine, vincristine and irinotecan liposomes were prepared at adrug/lipid ratio of 2:9.58, as described in Example 2 with exception ofthe replacement of SBE-β-CD/TA with (NH₄)₂SO₄ for (NH₄)₂SO₄ as innerwater phase, as described in Example 2 for SBE-CD/TA as inner waterphase, and as described in Example 2 with exception of the replacementof SBE-β-CD/TA with SBE-β-CD/NH₃ for SBE-CD/NH₃ as inner water phase.

2, Animals and Dosage

This example was conducted in male DBA/2 mice, and the dosage was 10mg/kg.

3, Results

TABLE 5 Plasma pharmacokinetics of liposome formulations havingdifferent inner water phase Half-life for different drug liposome (h)Inner water phase Vinorelbine Vincristine Irinotecan SBE-CD/TA 4.4 67.38.6 SBE-CD/NH₃ 5.4 46.2 11.3 (NH₄)₂SO₄ 3.1 27.6 4.1

Conclusion: As shown in pharmacokinetic results, in comparison to theliposome having ammonium sulfate as inner water phase, the liposomeshaving SBE-CD/NH₃ as inner water phase exhibit significantly extendedhalf life.

Example 11 Efficacies of Vinorelbine Liposomes Having Different InnerWater Phase on LLC Tumor Model

1, Formulations

Formulation 1: SBE-CD/TA as inner water phase, prepared as described inExample 2.

Formulation 2: Ammonium sulfate as inner water phase, prepared asdescribed in Example 2 with exception of the replacement of SBE-β-CD/TAwith ammonium sulfate.

In both formulations, drug/lipid ratio is 3:9.58, and the content ofDSPE-mPEG2000 is 0.5%.

2, Experiments

LLC lung cancer cells were collected, and diluted with DMEM medium.After dilution, the tumor cell number was modulated to 2.0×10⁶ cells/ml.0.2 mL of the tumor cell suspension containing about 4×10⁵ tumor cellswas inoculated into forward limb oxter subcutaneous tissue of female C57mice under aseptic condition. Fourteen days after inoculation, mice wererandomized by tumor volume into three groups and administered with asingle i.v. injection at a dose of 10 mg/kg.

The mice were bred normally after administration. Tumor diameters weremeasured to dynamically evaluate anti-tumor efficacies of differentformulations. Tumor volume (TV) was calculated with the followingformula:TV=½×a×b ²,in which a and b represent length and width, respectively.

The tumor volumes were calculated by using the measurement results. Theexperiment data were analyzed using SPSS 11.5 statistics software.

3, Results

TABLE 6 anti-tumor efficacies of vinorelbine liposomes having differentinner water phase on LLC tumor model (n = 10, x ± sd) Day after Tumorvolume (mm³) administration SBE-CD/TA ammonium sulfate 5% glucosesolution 0 785.0 ± 343.0  692.2 ± 259.3  780.8 ± 353.3 1 1214.5 ±732.4   979.7 ± 507.3  1154.8 ± 618.0  2 1179.6 ± 730.0   940.7 ± 415.1 1378.2 ± 753.2  3 1420.5 ± 716.3   1116.8 ± 503.5   1964.3 ± 1004.2 41591.6 ± 1056.1  1091.6 ± 562.3**  2456.5 ± 1170.1 6 1665.2 ± 1121.3* 1353.7 ± 631.6**  3173.9 ± 1591.2 7 2034.7 ± 1233.8*  1846.7 ± 1051.5**4117.7 ± 2022.8 9 1939.0 ± 1171.0** 2086.5 ± 1446.8** 4715.0 ± 2203.6 112605.2 ± 1683.3** 3142.4 ± 1643.0*  6307.6 ± 3194.9 12 2893.5 ± 1656.5**3650.4 ± 1931.8** 7562.9 ± 3819.7 14 3793.5 ± 2671.7** 5106.1 ± 2465.1**9464.8 ± 4151.7 **P < 0.01, *P < 0.05, in comparison with 5% glucosecontrol

In comparison with 5% glucose, the growth of tumor was significantlysuppressed from day 4 for the liposomes having ammonium sulfate as innerwater phase and from day 6 for the liposomes having SBE-CD as innerwater phase.

Relative tumor proliferation rate T/C (%) was calculated with thefollowing formula: T/C %=TRTV/CRTV×100%, in which TRTV and CRTVrepresent relative tumor volume (RTV) of treatment group and of negativecontrol group, respectively. RTV=Vt/Vo. Vo means tumor volume of day 0(initial dosage), and Vt means tumor volume at each measuring day.Regarding relative tumor volume proliferation rate of SBE-CD group andammonium sulfate group, the lowest T/C % were 51.8% and 31.1%respectively. That is, anti-tumor efficacy of SBE-CD group on LLC lungcancer was superior to that of ammonium sulfate group.

Example 12 Anti-Tumor Efficacies of Topotecan Liposomes Having DifferentInner Water Phase on Prostate RM-1 Tumor Model

1, Formulations

Formulation 1: SBE-CD/TA as inner water phase, prepared as described inExample 2.

Formulation 2: Sucrose octasulfate as inner water phase, prepared asdescribed in Example 2 with exception of the replacement of SBE-β-CD/TAwith sucrose octasulfate.

In both formulations, drug/lipid ratio is 3:9.58, and the content ofDSPE-mPEG2000 is 0.5%.

2, Experiments

RM-1 lung cancer cells were collected, and diluted with 1640 medium.After dilution, the tumor cell number was modulated to 2.0×10⁶ cells/ml.0.2 mL of the tumor cell suspension containing about 4×10⁵ tumor cellswas inoculated into forward limb oxter subcutaneous tissue of female C57mice under aseptic condition. Twelve days after inoculation, mice wererandomized by tumor volume into groups and administered with a singlei.v. injection at a dose of 10 mg/kg.

The mice were bred normally after administration. Tumor diameters weremeasured to dynamically evaluate anti-tumor efficacies of differentformulations. Tumor volume (TV) was calculated with the followingformula:TV=½×a×b ²,in which a and b represent length and width, respectively.

The tumor volumes were calculated by using the measurement results. Theexperiment data were analyzed using SPSS 11.5 statistics software.

3, Results

TABLE 7 The antineoplastic effects of topotecan liposomes on RM-1 tumourmodel (n = 10, x ± sd) Tumor volume (mm³) Day after Sucrose Free 5%glucose administration SBE-CD/TA octasulfate topotecan control 0 220.1 ±70.1  218.8 ± 67.3   223.0 ± 65.7  219.6 ± 60.2  2 339.2 ± 145.0* 336.8± 96.3*  484.0 ± 154.7 468.9 ± 137.7 4 397.3 ± 234.4* 347.0 ± 117.8**606.0 ± 183.1 765.3 ± 415.2 6  483.1 ± 253.6** 500.3 ± 165.5** 1060.7 ±393.0  1376.9 ± 689.3  8 690.2 ± 656.7* 640.7 ± 280.7** 1301.8 ± 563.7 2082.9 ± 1508.7 9 914.0 ± 691.4* 734.2 ± 343.6*  1628.5 ± 835.4  2598.7± 2148.2 13 1876.2 ± 1931.9* 1247.8 ± 858.7**  3592.9 ± 1523.5 4499.4 ±2946.5 15 2833.9 ± 3016.7* 2571.1 ± 2844.9** 6639.3 ± 2388.2 7504.9 ±4335.9 **P < 0.01, *P < 0.05, in comparison with 5% glucose controlgroup

In comparison with 5% glucose for injection as control, free topotecandid not significantly suppress the growth of tumor (p>0.05), while thetumor growth was significantly suppressed in the two groups of theliposomes having different inner water phase. Significant differenceswere observed in comparison with free topotecan groups with equaldosages, while no significant difference of the suppression on RM-1tumor was observed between the two liposomal formulations.

Example 13 Toxicity of Different Liposomal Topotecan Formulations in KMMice

1, Formulations

Formulation 1: SBE-CD/TA as inner water phase, prepared as described inExample 2.

Formulation 2: Sucrose octasulfate as inner water phase, prepared asdescribed in Example 2 with exception of the replacement of SBE-β-CD/TAwith sucrose octasulfate.

In both formulations, drug/lipid ratio is 3:9.58, and the content ofDSPE-mPEG2000 is 0.5%.

2, Experiments

Regarding the three liposomal drugs and free drug, each dosage group hastwo female KM mice, beginning with a maximum dose of 40.6 mg/kg oftopotecan and continuing with a descending dose factor of 1.25 (i.e.dosages: 40.6, 32.5, 26.0, 20.8, 16.6, 13.3 and 10.6 mg/kg). Mice wasobserved in terms of general health and weighed every day for a periodof 14 days.

TABLE 8 toxicity of liposomal topotecan formulations having differentinner water phase Number of Animals number of dead animals with >15%weight loss Dosage Sucrose Sucrose level SBE- octa- Free SBE- octa- Free(mg/kg) CD/TA sulfate topotecan CD/TA sulfate topotecan 40.6 1 2 1 2 2 232.5 1 2 — 2 2 1 26.0 — 2 — 2 2 — 20.8 — 2 — 2 2 — 16.6 — 2 — 2 2 — 13.3— 1 — 2 1 — 10.6 — 1 — 2 1 —

As shown in Table 8, the order of toxicity was: free topotecan<liposomehaving SBE-CD/TA as inner water phase<liposome having sucroseoctasulfate as inner water phase. The sucrose octasulfate liposomecaused animal death in a relative low dosage.

The present inventors further prepared the liposomes of vinorelbine,vincristine and irinotecan, and similarly evaluated their toxicities inKM mice. The same results as that of topotecan were obtained. The orderof toxicity was: free drug<liposome having SBE-CD/TA as inner waterphase<liposome having sucrose octasulfate as inner water phase. Thesucrose octasulfate liposome caused animal death in a relative lowdosage.

What is claimed:
 1. A liposome comprising bilayer, inner water phase andmetal cation ionophore in the outer phase, wherein the inner water phasecomprises sulfobutyl ether cyclodextrin, one or more active compoundsselected from the group consisting of doxorubicin, epirubicin,pirarubicin, idarubicin and mitoxantrone, and one or more of sodium ion,potassium ion and calcium ion, wherein the sulfobutyl ether cyclodextrinforms precipitate with the active compound in the inner water phase. 2.The liposome according to claim 1, wherein the metal cation ionophore isselected from the group consisting of nikkomycin, A23187 and ionomycin.3. The liposome according to claim 1, wherein the sulfobutyl ethercyclodextrin is sulfobutyl ether-α-cyclodextrin, sulfobutylether-β-cyclodextrin or sulfobutyl ether-γ-cyclodextrin.
 4. The liposomeaccording to claim 1, wherein the sulfobutyl ether cyclodextrin hasabout 6.5 sulfo groups at average per molecule.
 5. The liposomeaccording to claim 1, wherein the bilayer comprises phospholipid,cholesterol and hydrophilic polymer-modified lipid.
 6. A liposomecomprising bilayer and inner water phase, wherein the inner water phasecomprises sulfobutyl ether cyclodextrin, one or more active compoundsselected from the group consisting of doxorubicin, epirubicin,pirarubicin, idarubicin and mitoxantrone, and one or more of ammoniumhydroxide, triethylamine and triethanolamine, wherein the sulfobutylether cyclodextrin forms precipitate with the active compound in theinner water phase.
 7. The liposome according to claim 6, wherein thesulfobutyl ether cyclodextrin is sulfobutyl ether-α-cyclodextrin,sulfobutyl ether-β-cyclodextrin or sulfobutyl ether-γ-cyclodextrin. 8.The liposome according to claim 6, wherein the sulfobutyl ethercyclodextrin has about 6.5 sulfo groups at average per molecule.
 9. Theliposome according to claim 6, wherein the bilayer comprisesphospholipid, cholesterol and hydrophilic polymer-modified lipid.
 10. Aprocess for preparing the liposome according to claim 1, comprising: (1)hydrating lipid phase powders with a first aqueous solution of asulfobutyl ether cyclodextrin salt that comprises one or more of sodiumion, potassium ion and calcium ion, to form a blank liposome comprisingthe first aqueous solution of the sulfobutyl ether cyclodextrin salt asinner water phase, (2) removing the salt of sulfobutyl ethercyclodextrin in the outer phase of the blank liposome, to form an aniongradient, (3) adding a metal cation ionophore to the outer phase of theblank liposome, to form a pH gradient, and (4) incubating the blankliposome with the active compound in a second aqueous solution, toencapsulate the active compound into the liposome.
 11. A liposomalpharmaceutical preparation, comprising the liposome according to claim 1and a pharmaceutically acceptable carrier and/or excipient.
 12. Aliposomal pharmaceutical preparation according to claim 11, wherein thecarrier and/or excipient comprises osmotic regulator and/or antioxidant.13. A method of treating a tumor patient, comprising administering aliposome according to claim 1 to the patient in need thereof.